03. Pharmacokinetics Flashcards
When considering absorption of drugs from the gastrointestinal (GI) tract
- thiopental cannot be administered through a GI tract route.
T/F?
False. Can be given PR, absorbed well.
Neostigmine is better absorbed from the GI tract than physostigmine. T/F
False.
Neostigmine is quaternary and charged,
physostigmine is a tertiary amine
Which of the following drugs bind more to alpha-1 acid glycoprotein than to albumin:
diazepam fentanyl phenytoin ibuprofen lidocaine
fentanyl and lidocaine.
In general acidic/neutral drugs bind to albumin and basic drugs or those with a quaternary nitrogen, to alpha-1 acid glycoprotein.
Lidocaine and fentanyl are basic drugs, ibuprofen is acidic and diazepam/phenytoin are neutral - they are not water soluble.
T/F:
The interaction between amiodarone and warfarin is entirely due to competition for plasma protein binding sites.
False.
This interaction is mainly due to a metabolic interaction: amiodarone inhibits CYP2C9
T/F: Non-depolarizing muscle relaxants have a smaller volume of distribution than induction agents
True.
ndmrs are charged molecules and do not cross lipid membranes so have relatively small volumes of distribution
Forumla to calculate Vd in one-compartment model?
volume of distribution is given by clearance divided by rate constant for elimination
(Vd = Cl/k)
Which of these enzymes show the most significant pharmacogenetic variation?
CYP2E1 CYP2D6 CYP3A5 CYP2C9 CYP1A2
CYP 2D6 - metabolism of codeine conversion to morphine.
CYP 2C9 - metabolism of S-warfarin
26 + 29
Mivacurium elimination?
mivacurium is broken down by butyrylcholinesterase,
cisatracurium and atracurium are degraded by the Hofmann process
True or false:
For a ONE compartment model, after giving an intravenous bolus dose, the rate of elimination at a particular time is dependent only on the clearance.
False.
It is proportional to plasma concentration - an exponential relationship - whereas clearance is constant
rate of elimination proportional to plasma concentration.
True or false:
in a ONE compartment model, the behaviour of the drug can be predicted as long as the clearance is known.
False.
To know the behaviour of a drug, you need to know:
- volume of distribution
- time constant (or rate constant for elimination)
In a 3 compartment model, what are the most important factors to determining the variability of the CSHT?
- duration of the infusion.
- the ratio of elimination to redistribution.
When considering elimination of drug from the body:
if glomerular filtration rate doubles, then the amount of free drug excreted through the urine also doubles?
False,
urinary elimination depends also on tubular secretion.
When considering elimination of drug from the body:
Hepatic enzymes involved in xenobiotic metabolism are exclusively associated with the smooth endoplasmic reticulum.
False.
There are CYP enzymes in the SER, but metabolic enzymes are also found in the cytoplasm (alcohol dehydrogenase) and associated with mitochondria (MAO).
In patients with hepatic failure and ascites:
The bioavailability of drugs with a moderate heptic extraction ratio is increased or decreased?
The bioavailability increases - metabolic capacity will be reduced as may hepatic flow.
Which of the following will increase hepatic extraction of propofol:
Dobutamine Ciprofloxacin Carbamezapine Noradrenaline Chronic alcohol intake
Dobutamine - increases hepatic blood flow.
